In recent years as energy conservation and environmental issues are increasingly discussed, electric vehicles are increasingly noted. Electric vehicles are vehicles having as a source of power a direct current (dc) power supply, an inverter, and a motor driven by the inverter.
One such conventionally known electric vehicle is a fuel cell vehicle employing a fuel cell for a dc power supply. Generally a fuel cell vehicle is equipped with a secondary battery for recovering energy regenerated by a motor in a regeneration mode, and uses the regenerated power to charge the secondary battery and uses the fuel cell and the secondary battery together to supply power of high voltage to the motor.
More specifically in such fuel cell vehicle the motor is generally implemented by an alternating current (ac) motor and the fuel cell and/or the secondary battery output(s) dc power which is in turn converted to ac power and supplied to the ac motor, and when the ac motor regeneratively operates it generates ac power which is in turn converted to dc power charging the secondary battery, and furthermore the fuel cell outputs dc power which is converted in voltage to a prescribed dc voltage to charge the secondary battery. Thus between the fuel cell, the secondary battery and the ac motor a variety of voltage conversions is effected.
Conventionally, such conversion of power between a plurality of dc power supplies and an ac motor has generally been performed by a power conversion device that combines an inverter performing dc-ac conversion and a converter performing conversion in voltage between direct currents.
In recent years, matrix converter has been noted as a new power conversion device. Generally it is known as a converter capable of directly converting an alternating current to an alternating current without temporarily converting it to a direct current. For example, it is well known as bi-directional switches arranged in a matrix of three rows and three columns and directly converting a prescribed 3-phase ac voltage output from a 3-phase ac power supply to a 3-phase ac voltage of any voltage and frequency.
Such a matrix converter is employed in an electric system, as disclosed in U.S. Patent Application Publication No. 2001/0026427, which discloses an overvoltage protection device employing a matrix converter.